It doesn't say clear cut that it is strong, and if you mean to day that it is so high in order and that is why we should call it strong, note that you are not seeing an exhaustive list and several ligands have been skipped in between (like o-phenanthroline etc.)

And @Ayan_Agrawal, oh no problem, lets search for it together😀. What did you do in the exam btw? (I did D)@Gurnoor_Singh any opinions bro?

I was about to go for D then ended up with C.
I read the upper link and by according to it NH3 is moderate field ligand but for cases like Cobalt it acts as Strong Ligand.
But it is more of data based question.